Casting process



March 17, 1959 0 SCHAABER CASTING PROCESS Filed Aug. 27,- 1955 2 Sheets-Sheet 1 ESSION BAUMANN SULPHUR |M PR ISOLIDIFI ED AFTER ROTARY MAGN APPLIED ETIC FIELD R CONTENT HIGH SULPHU TL W NA Y ET F TS EA NY ST R 0 6 DR Y EF RR F0 W m PM LR .H UP %A S C RS SU mum w PD CA .MAGNETIC FIELD POOR .SULPHUR com'uT FIG.I

OLIDIFIED AFTER APPLIED OTARY MAGNETIC FIELD SULPHUR CONTENT souomeo CRUST INVENTOR OTTO SGHAABER NARROW 20m: OF POOR INTERM APPLIE AT'I'ORNEYJ March 17, 1959 o.- SCHAABER 2,877,525 CASTING PROCESS Filed Aug. 27, 1953 ZSheets-Sheet 2 RST RST

INVENTOR ATTORNEYJ' CASTING PROCESS Otto Schaaber, Schorndorf, Wurttemberg, Germany Application August 27, 1953, Serial No. 376,917

6 Claims. (Cl. 221-2001) This invention relates to a casting process of the particular kind, in which the melt as it solidifies is subjected to the action of magnetic rotary fields for influencing the structure of the solidified casting. Extensive research has shown that it is not necessary but may be even detrimental to subject the melt to the action of these fields until it has solidified completely. It is sufiicient if the action is limited to a fraction of the solidifying period.

A lasting effect on the structure of the finished casting could quite unexpectedly be noticed if the rotary. field is also repeatedly interrupted during period of action which is already relatively short compared with the total time of solidification. The total period of action is further reduced by such a measure, from which various results and advantages of a technical nature are obtained which are hereinafter described.

The accompanying drawings serve to illustrate this description and show:

Fig. l a Baumann impression of the cross-section of a 100 x 100 mm. square bolt with wide annular zone poor in sulphur,

Fig. 2 a Baumann impression similar to that shown in Fig. l with a narrow annular zone poor in sulphur,

Fig. 3 a longitudinal section thru a continuous casting with rotary field arrangement,

Fig. 4 is a top plan view of Fig. 3.

While it was originally believed thatto improve the structure of the finished casting with the aid of the rotary field this must be allowed to act continually until the state of complete solidification is reached, it was a step in the right direction to have recognized that the action of the rotary field can be limited to a fraction of the total time of solidification and preferablyto less than 5% thereof. Furthermore, according to the knowledge revealed by the present invention, it is possible and advantageous to also-interrupt repeatedly'the magnetic rotary field during the period in which it acts and which is short as compared with the total time of solidification;

whereby the duration of the intervals maybe shorter than, equal to or longer than the time during whichlthe field is switched on.

The total period during which the rotary field is acting is thus restricted as a rule to times which are con siderably shorter than 5% of the total time ofsolidification. For example, the shrinkage depth in around steel bolt 118 mms. in diameter amounts under certain casting conditions to roughtly 3.5 m. in the case of a casting speed of 700 mms./min. The total time of solidification can thus be reckoned as 5 minutes. In one of the above mentioned experiments with an interrupted rotary field it was discovered from the evaluation of the characteristic effect of the field, which will be referred to later, that three periods of action each of 1.8 seconds duration had sufiiced to obtain the said improvement in structure. The total time of action of 5.4 seconds resulting therefrom is only 1.8% of the total period of solidification. For safety reasons, however, it is usual to allow the field to act longer.

The advantage consists in the saving of energy and, if several casting molds are to be served, in the saving of installation costs, because several rotary fields can be operated successively with a single transformer plant.

' When casting-steel under the action of a magnetic rotary field, the applicant noticed the curious phenomenon that those zones which during the time the rotary field is in operation, have just reached a certain range of temperature, show a slightly lower sulphur content than the neighbouring zones. The difference is not great, for example it was found that the sulphur content in the non-influenced zones on the average of five readings in each case 0.051% S, in the zone covered by the rotary field in the corresponding temperature range 0.046%, and in the core structure 0.056% S. The zone influenced by the rotary field is, however, easily recognisable from the sulphur impression according to Banmann in spite of this slight difierence. For example Fig. 1 shows a Baumann impression of the cross-section of a 100 x 100 mm. square bolt with an analysis 'of 0.07% C, 0.1% Si, 0.28% Mn, 0.118% P, 0.035% S; the remainder being iron which was cast under the following conditions: casting temperature at the beginning was 1540" C. and 1430 C. at the end, relay field, three poles on rotary current; core 120 x 120 mms.; ten windings of fiat copper stood on edge; lying directly in water; interlinked voltage; 27 v. coil current; 950 to 1000 amp. pha'seload; 1630to 1730 amp.; two parallelconne'cted variable transformers each kva.; primary side 19.8 kw. consumption. The arrangement for producing the magnetic. rotary current was located below and independently of the chill.

The formation of the somewhat poor sulphur zones vunder the influence of the rotary field is possibly conmelt from the edge under the action of the temperature gradient. These primary crystals are themselves poorer 'n sulphur than the 'remainer of the melt, which, in the case of undisturbed crystallation .solidifies somewhat later in the spaces between the primary crystals. During the time when the rotary field isoperative, the primary on the Baumann impression, with the zone ofthe deto thedirection of rotation. growing crystals is followed by the larger :inrler zone,

crystals grow inwardly'jbiased in the opposite direction The zone with. the biased the crystallization of which .under the previous action of the rotary field, takes place without biased orientation. A comparison of 'the lighter zones poor in sulphur flected crystal ends of the 'microsection surfaces shows that these two zones correspond as regards their position and are therefore identical.

The crystal points projecting into the melt are consequentlynot rubbed off by the action of the rotary field, as was vformerly erroneously imagined, but they are bent over and, then cease'altogether. During the deflection in counter-direction to the direction of rotation of the field, the crystals lie more closely together. Consequently there remains very little space between them in which the remainder of the melt, which is richer in sulphur, can solidify. This layer poor in sulphur caused by the action of the rotary field, is not identical with the less stable layer also poor in sulphur which is to be observed in slow cooling ingot casting, and which there indicates the transition from the directed edge solidification to the undirected core solidification. The physical properties of the layer poor in sulphur produced by the rotary field are the same as those in the surrounding layers.

Nevertheless the presence of such zones poor su1-.

can be seen from' Fig. .2, is less than. a millimeter in width (casting condition).

. As arule-itis recommended inthezcaserof short-time rotary field action .to .increasethe .energy of :the rotary :field surge as compared with ..that .usedv for continual action.

Fig.2 shows the resultof. a short-time rotary field :action; the conditions were: Analysis-0.12% C; 0.14%

Si; 0.31% Mn; 0.1% .P;l 0.36% :S; rotary. field. action 2.4 secs., interval 20,secs.; rotary field strengthv 1.9.8 kw.; test arrangement as above.

The :utilization of knowledge on which the: applicamelting point-with which the sump depth is great compared with that of low melting metals, .such as light metals, that is, .is' at. least ten percent .greater. In :this

:tion is based in continuous casting presents particular advantages, especially when casting metals with a high case it is not necessary for the rotary fieldto act on the entire depth of the sump, which, for example in the case :of a bolt 100x. 100 mms. maybe 3,000 mms.;. a shortzone. of action will suffice,which is preferably less than 5% of the sump depth. Thiszallows considerable freedom from .a constructional point of view, because thearrangement of the rotary field can bestructurally united with the cooling 'jacketofthe casting ,moldzor arranged :entirely underneath the casting mold. To :accommodate ithe. iron cross-section" of.. themore :for :asufliciently strong rotary-field, necessitates a-certain minimum height-for.the-rotary :field. amuleztthe height can be taken as about 150 rnms. including the coil, inthe case of rotary fields for influencing cross sections of 100 to 120 rnms. When the rotary field is switched full on the effective height of the rotary field is determined by this height which must also-be multiplied by a factor dependent upon the actual field strength.

As,-however, it is also dependent upon'the temperature and the composition of the melt, the effective height .can be most easily determined byexperiment. Thereffec- 'tive height of the rotary fieldswcan be calculated from the width of the zone poor in sulphur, for example about 4-mms. .in Fig- 1, if from other experiments-or calculations thetimeis known-which is: required to cause Qthe' solidification. of :4 mms, in the example rshownsin Fig-:1. From these-measurements the time can'bc esti- A form of construction of a continuous casting plant with rotary field arrangement according to the invention, is illustrated in Figs.-3 and 4 of the drawings. 1 designates a casting ladle, from which the metal jet 2 drops into the cooled thru-fiow chill 3; 4 is the string which on leaving the chill 3 comes within the range of the rotary field arrangement 5 and is subsequently gripepd by the conveyor rollers 6. The coils 5a, 5b, 5c of the rotary field poles 7a, 7b, 7c. are connected to the network 10 over the interrupter 8 and the transformer 9. The interrupter 8 switches the transformer onto the network 10 for a certain period of time with the aid of a known combination of time relays and magnetic switches, then interrupts the connection with the network for an adjustable predetermined period, in order to once more switch on the transformer. The string 4 is subjected to the action of the magnetic rotary field only for the-period during which the interrupter 8 establishes the connection between the network and the transformer 9. In the sectional illustration of the string .4 ..the time markings becoming visible by subsequent development (production of longitudinal or transverse r microsection surfaces and the etching thereof) are indicatedjby the lines extending parallel with the solidification face.

I claim: .1.'A casting processin which the molten metal is :subjected to the application of magnetic rotary fields .duringsolidification for the purpose of influencing the crystallization of the metal, comprising applying .the

.magnetic rotating field transversely across the molten metal core constituting the major area within a solidified crust and in the order of five percent of-thecomplete :metal. solidification time and before the end of the solidification period.

.2. .A casting process as in claim 1, comprising interimitten'tly applying said magnetic rotating field.

3. A casting process as in claim 2, comprising reversriingthe. direction ofrotation of said magnetic field upon 'mated at about 35-secdn'ds. '1(This'..makes the'Fetfective height of the rotary field'350 mmszzatanassumed casting speed of 600 mms./min.). .The'35 *seconds are;-accordingto the .knowledge' 'obtained by the inventor;- even more :.than is considered necessary for the periodof action. For this reason :a periodical interruption :ofthe rotary field is recommendedin this :case.

every intermittent application of said field.

4. A casting process as in claim 1, comprising applying said magnetic rotating field to metal being continuously cast.

5. A casting process as in claim 4, comprising applying said rotating magnetic field directly below the upper surface of the molten metal in a continuou casting mold.

6. A casting process as in claim 5, comprising said magnetic field to substantially only five percentof the height of the molten core of the ingot being cast in the mold.

I References .Cited'in the file. of patent UNITED STATES PATENTS 

1. A CASTING PROCESS IN WHICH THE MOLTEN METAL IS SUBJECTED TO THE APPLICATION OF MAGNETIC ROTARY FIELDS DURING AOLIDIFICATION FOR THE PURPOSE OF INFLUENTCING THE CRYSTALLIZATION OF THE METAL, COMPRISING APPLYING THE MAGNETIC ROTATING FIELD TRANSVERSELY ACROSS THE MOLTEN METAL CORE CONSTITUTING THE MAJOR AREA WITHIN A SOLIDIFIED CRUST AND IN THE ORDER OF FIVE PERCENT OF THE COMPLETE MELAT SOLIDIFICATION TIME AND BEFORE THE END OF THE SOLIDIFICATION PERIOD. 